New York police ask FBI serial killer profilers for help after the shooting deaths of three older men of Middle Eastern descent are linked to one gun.

With a single gun linked to the fatal shootings of three Brooklyn shopkeepers since July — each of Middle Eastern descent — New York police have asked for help from FBI experts who profile serial killers.

The latest killing took place Friday night, when Rahmatollah Vahidipour, 78, was gunned down inside his boutique in the Flatbush neighborhood.

"In the past three nights, police officers and detectives were here questioning, trying to get a clue, trying to investigate," Abraham Shokirian, a son-in-law of Vahidipour, said in a phone interview Tuesday. "The best thing you can hope for is that these things don't happen to another grandfather, to another family."

Vahidipour was shot three times in the head and torso about an hour before his clothing shop was to close for the evening. Police said ballistics tests matched shell casings found at the scene to a .22-caliber gun used in the Aug. 2 killing of Isaac Kadare, 59, and the July 6 shooting of Mohamed Gebeli, 65.

Police said Tuesday night that they were interviewing a man they dubbed "John Doe Duffel Bag" — a mustachioed, bag-toting white male seen on surveillance video taken near the site of Friday's shooting. He had also been seen near one of the earlier killings, a police spokesman said in an email to The Times.

Police were looking for three other people also seen on the video, but said that none of the four were suspects — only potential witnesses who could offer valuable information.

Police on Monday asked the FBI for help in the investigation.

"The FBI will be providing assistance, to include expertise from the Behavioral Analysis Unit," Martin Feely, the FBI's New York bureau supervisory special agent, said in a statement, referring to experts who profile criminals, including serial killers. "The New York Police Department remains the lead investigative agency."

Vahidipour was of Iranian descent; Kadare and Gebeli were Egyptian, according to local news reports.

In all three killings, the victims were working alone at businesses without security cameras inside.

Each time the killer moved the victim's body so it couldn't be easily noticed, police said.

Vahidipour's body was dragged to the back of his store, the She She boutique, and hidden under clothes, police said, adding that nothing was stolen from the store.

In the August slaying, in the Bensonhurst neighborhood, Kadare was shot once above an eye and stabbed three times in the neck. His face was covered with an aluminum tray and bleach was splashed on his pants.

In July, Gebeli was shot once in the neck; his body was discovered under a pile of unspecified merchandise inside his Bay Ridge shop.

"I'm sure he's not in his right mind," Shokirian, Vahidipour's son-in-law, said of the killer. "Put him away — put him in solitary, put him in house arrest, put him in jail — to make him not commit this sort of crime again."